A Mystery of Space: S T A R S- [The Study of the Sun]

Up until 1611, the sun was looked at as a important body in the sky, but was never studied as a physical object. The first to do so, in 1611, was Galileo Galilei(1564-1642), an Italian astronomer and physicist.

Galileo, as painted by Justus Sustermans in 1636

He used the newly invented telescope to study the surface of the sun. Galileo noted that there were dark spots on the sun, which was the first "physical study" of the sun. From then on, people looked at the sun scientifically, and started to study it.
In 1814, German physicist Joseph von Fraunhofer was using a spectroscope (which breaks up the light that you see into its component wavelengths, or colors), which made it possible to make a theoretical explanation of the solar atmosphere.
In 1859, another German physicist, Gustav Kirchoff, was studying the sun, with a spectroscope, and discovered, using Fraunhofer's spectrum (the dark lines in the solar (sun) spectrum), that the sun was made of some elements found present on Earth. Since the sun was found to be made of mostly ordinary matter, then it could be studied in great detail, and, if the information the sun provided could be analyzed, then that information could be used for finding what the other objects in the universe were made of, and how they worked. This breakthrough was the beginning of astrophysics.